Modification of poly(lactic acid) films: Enhanced wettability from surface-confined photografting and increased degradation rate due to an artifact of the photografting process

The major objective of this research was to modify PLA film surfaces with the ultimate aim of making a bioactive surface that will show faster degradation. The PLA film was solvent-cast, and the film surfaces were grafted with poly(acrylic acid) (PAA) and poly(acrylamide) (PAAm) using a UV-induced photopolymerization process. The film surface resulting from each reaction step was analyzed using ATR-FTIR spectroscopy and contact angle measurements. Results showed that PAA was grafted from PLA film surfaces in 2 or 3 h, while PAAm was grafted in 3 or 5 h depending on the method of activation. Films grafted with PAA and PAAm exhibited improved wettability. The neat and surface-modified films were incubated in different pH solutions, viz., pH = 4, 7, and 10, for specified time periods. The films resulting from each treatment were analyzed using atomic force microscopy (AFM). The molecular weights of the incubated films were measured using chloroform-based GPC. Results established that faster degradation of the PLA film when incubated in different pH solutions was achieved for PLA-g-PAA films; however, control studies revealed that the major contribution to the observed degradation was due to the entangled PAA chains resulting from acrylic acid monomer that migrated into the film bulk and not due to the surface-grafted layers.